This invention relates to methods and apparatus for providing a breathable gas mixture for use in a hostile environment and, more particularly, to a semiclosed-loop rebreather system for removing carbon dioxide and metabolically induced moisture from air exhaled by the user while further providing for radiation dissipation of heat generated during the carbon dioxide removal. While the invention will be described with particular reference to systems used by astronauts, it is to be understood that this invention is applicable to other fields which require that a breathable gas mixture be supplied to the user.
Portable breathing systems are used to enable men to perform tasks in hostile environments such as those containing noxious gases inimical to life support or in those lacking sufficient oxygen to support life. Thus, portable breathing systems find use in such varied occupational areas as space flight and fire fighting, both of which require an adequate supply of breathable gas supplied at normal breathing temperatures and humidities and free from contaminants. In recent years various such devices have been developed and in general fall into three categories.
One such category is the compressed air system consisting of a large compressed air tank feeding a demand regulator which provides a breathable gas mixture to a mask during inhalation, which exhaled air being vented out of the mask. The two major problems with this type of system are excessive total weight and short operating time, both of which may be overcome by replacing the compressed air tank with a supply hose connected to a remote source of breathing gas which, while reducing the weight of the system and increasing the operating time, has a disadvantage of restricting the user to an area defined by the length of the supply hose.
Another category is the closed-loop rebreather system, such as disclosed in U.S. Pat. No. 3,942,524, in which exhaled air is passed through a chemical bed of the superoxides, for example, potassium superoxide, which reacts with the exhaled air to remove carbon dioxide contained therein. At the same time, oxygen is released which is mixed with exhaled air and the mixture supplied to the user for rebreathing. The problem with this type of system is that the reaction of the moist warm air with the superoxide creates a slurry of melted potassium superoxide with the attendant requirement to remove the slurry prior to presenting the air for rebreathing. Additionally, the adsorption of the gas by the superoxide produces a reaction heat which must be dissipated prior to rebreathing. Thus, heat is dissipated through connection with the baffled breathing bag.
The third general category is the semiclosed-loop rebreathing system, such as disclosed in U.S. Pat. No. 3,923,053, consisting of a breathing bag, a chemical scrubber, such as a molecular sieve material for removing carbon dioxide, and an outside source of oxygen or breathing gas either in a gaseous or liquid state. Initially, the breathing bag is filled and the wearer inhales directly from the breathing bag and exhales through the carbon dioxide scrubber back into the breathing bag. The breathing gas from the outside source is slowly leaked into the bag to provide for system losses from metabolically used oxygen. The problems with such systems are the high temperature of the inhaled gas caused by the chemical reaction with the molecular sieve material and the impedance to breathing caused by the build-up of carbon dioxide in the sieve material itself. In an attempt to reduce the heat caused by reaction of moisture contained in the exhaled gas, a desiccant is interposed between the user and the scrubber.
The disadvantages of the prior art are overcome with the present invention and a portable breathing system is herein provided which is not only fully capable of providing revitalized exhaled air for rebreathing thereof, but which is also fully capable of other tasks completely beyond the capabilities of the prior art devices and systems. More particularly, however, the system of the present invention is capable of providing revitalized exhaled air for rebreathing and at temperatures and humidities normal for breathing.